Two polyketide synthase-encoding genes are required for biosynthesis of the polyketide virulence factor, T-toxin, by Cochliobolus heterostrophus

Mol Plant Microbe Interact. 2006 Feb;19(2):139-49. doi: 10.1094/MPMI-19-0139.

Abstract

Cochliobolus heterostrophus race T, causal agent of southern corn leaf blight, requires T-toxin (a family of C35 to C49 polyketides) for high virulence on T-cytoplasm maize. Production of T-toxin is controlled by two unlinked loci, Tox1A and Tox1B, carried on 1.2 Mb of DNA not found in race O, a mildly virulent form of the fungus that does not produce T-toxin, or in any other Cochliobolus spp. or closely related fungus. PKS1, a polyketide synthase (PKS)-encoding gene at Tox1A, and DEC1, a decarboxylase-encoding gene at Tox1B, are necessary for T-toxin production. Although there is evidence that additional genes are required for T-toxin production, efforts to clone them have been frustrated because the genes are located in highly repeated, A+T-rich DNA. To overcome this difficulty, ligation specificity-based expression analysis display (LEAD), a comparative amplified fragment length polymorphism/gel fractionation/capillary sequencing procedure, was applied to cDNAs from a near-isogenic pair of race T (Tox1+) and race O (Tox1-) strains. This led to discovery of PKS2, a second PKS-encoding gene that maps at Tox1A and is required for both T-toxin biosynthesis and high virulence to maize. Thus, the carbon chain of each T-toxin family member likely is assembled by action of two PKSs, which produce two polyketides, one of which may act as the starter unit for biosynthesis of the mature T-toxin molecule.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Ascomycota / enzymology*
  • Ascomycota / pathogenicity
  • Chromosome Mapping
  • Chromosomes, Plant / genetics
  • DNA, Complementary / genetics
  • Gene Deletion
  • Gene Expression Profiling
  • Macrolides / metabolism*
  • Microbial Sensitivity Tests
  • Multienzyme Complexes
  • Mycotoxins / biosynthesis*
  • Mycotoxins / chemistry
  • Phylogeny
  • Polyketide Synthases / chemistry
  • Polyketide Synthases / genetics*
  • Seedlings / microbiology
  • Sequence Analysis, DNA
  • Species Specificity
  • Virulence Factors / biosynthesis*
  • Zea mays / anatomy & histology
  • Zea mays / microbiology

Substances

  • DNA, Complementary
  • Macrolides
  • Multienzyme Complexes
  • Mycotoxins
  • Virulence Factors
  • Polyketide Synthases